1. Field of the Invention
The present invention relates to a V-type internal combustion engine in which a plurality of cylinders, spaced apart from each other in a V-shape, are provided on a crankcase. More particularly, the present invention relates to a V-type internal combustion engine including a control valve for an exhaust gas recirculation system (EGR), in which exhaust gas is recirculated into intake ports of the internal combustion engine to reduce nitrogen oxides (NOx) in the exhaust gas.
2. Description of the Background Art
With regard to internal combustion engines used for power sources of vehicles, such as motorcycles, it is know to use a V-type internal combustion engine in which a plurality of cylinders are disposed in a V-shape. The V-type configuration of the internal combustion engine makes it possible to make the internal combustion engine more compact, and reduce vibration resulting from the operation of the internal combustion engine, for example. In particular, for vehicles in which mounting space for the internal combustion engine is limited, such as motorcycles, the V-type internal combustion engine is known to be useful.
In addition, it is known to use an exhaust gas recirculation system (EGR) for recirculating exhaust gas into intake ports of an internal combustion engine, as well as a secondary air supply system for supplying secondary air into exhaust gas, for the purpose of cleaning the exhaust gas.
With regard to the secondary air supply system, an invention is known in which a secondary-air supply switching valve is disposed on the side opposite the direction of the offset of the rearward-inclined cylinder in a V-shaped space (V bank space) created between the cylinders of the V-type internal combustion engine. Placement of the valve in this location increases the cooling efficiency of the rearward-inclined cylinder, which is less prone to being blown against by the wind caused by vehicle travel, and also increases the cooling efficiency of the secondary-air supply switching valve. Such a configuration is disclosed, for example, in Japanese Patent Laid-Open No. 2002-89254.
In this type of system, a problem occurs in which the disposition of piping from an exhaust port side to an intake port side becomes complicated when the exhaust gas recirculation system is annexed to the internal combustion engine. In particular, optimal disposition of the EGR control valve is an issue when the exhaust gas recirculation system is annexed to the V-type internal combustion engine. Specifically, it is desirable to dispose the EGR control valve so that the V-type internal combustion engine becomes compact as a whole, without impairing the structural advantages of the V-type internal combustion engine.
An additional problem lies in that since, with regard to the V-type internal combustion engine, exhaust gas has to be recirculated to combustion chambers of the cylinders spaced apart in a V-shape, the structure of the internal combustion engine as a whole becomes complicated, and the internal combustion engine becomes large, unless the disposition, branching or the like of the recirculation channels of exhaust gas is contrived. In this case, an embodiment in which the EGR control valve is provided on each cylinder results in increase in the number of parts and increase in cost.
In an exhaust gas recirculation system, in order to prevent the ingredients of exhaust gas from attaching to wall surfaces of the recirculation passages, the exhaust gas must be maintained at a high temperature when recirculated into the combustion chambers, whereby the exhaust gas is efficiently cleaned. Accordingly, in addition to the size reduction mentioned above, it is desirable to find a way to recirculate exhaust gas while maintaining the recirculated exhaust gas at a high temperature. This is especially true when the V-type internal combustion engine is mounted on a motorcycle, since the degree of cooling of the internal combustion engine and the exhaust pipes by the wind caused by vehicle travel becomes large, it is very important to contrive a way to recirculate exhaust gas without much cooling.
The present invention has been made in consideration of the above described circumstances, and an object thereof is to provide, by disposing the EGR control valve annexed to the V-type internal combustion engine in a contrived manner, a V-type internal combustion engine which is compact as a whole, without impairing the compact structural advantage of the V-type internal combustion engine.
Another object of the present invention is to provide, in the same way, a V-type internal combustion engine which recirculates exhaust gas into the cylinders via a single EGR control valve, and, in addition, which makes it possible to minimize increase in the number of parts and increase in cost, and has a simple structure as a whole, by disposing and branching the recirculation channels of exhaust gas in a rational structure.
Still another object of the present invention is to provide, in the same way, a V-type internal combustion engine which can maintain high exhaust-gas cleaning efficiency by recirculating the exhaust gas at as high a temperature as possible, even if the internal combustion engine is cooled as the vehicle travels.